DE69023575T2 - New extruded films and foils made of polypropylene. - Google Patents

Description

Background of the invention 1. Field of the invention

The present invention relates to a novel extruded film or sheet formed by extruding a syndiotactic polypropylene having a syndiotactic pentad fraction of 0.7 or more or a syndiotactic propylene copolymer containing not more than 20% by weight of olefin units other than propylene units, wherein the olefin units contain 2 - 25 carbon atoms and the peak intensity of the propylene copolymer observed at 20.2 ppm on a 13C-NMR absorption spectrum measured in the form of a 1,2,4-trichlorobenzene solution using tetramethylsilane as a standard is at least 0.5 of the sum of all peak intensities corresponding to the respective methyl groups of propylene.

2. Description of the state of the art

Syndiotactic polypropylene itself has been known for many years. However, syndiotactic polypropylene prepared by low-temperature polymerization in the presence of a conventional catalyst and comprising a vanadium compound, ethers, and an organoaluminum compound exhibited low syndiotacticity and was hardly considered to have the characteristic properties of a syndiotactic polypropylene.

J. A. Ewen et al. were the first to establish that polypropylene with a tacticity greater than 0.7, expressed in syndiotactic pentad fraction measured by 13C-NMR, can be prepared by polymerizing propylene in the presence of a polymerization catalyst formed from a transition metal compound (Hf and Zr) with an asymmetric ligand and methylaluminoxane [J. Amer. Chem. Soc., 110, 6255 - 6 (1988)].

Isotactic polypropylene has a wide range of applications and, according to EP-A-0249 342, it can be used to produce extruded sheets and films. These sheets and films have relatively good physical properties, but have the problem that they have insufficient transparency. There has therefore long been a need for extruded polypropylene sheets and films with better transparency.

Summary of the invention

An object of the present invention is therefore the creation of novel extruded polypropylene films and extruded sheets with extremely good transparency and relatively good strength.

Further objects of the present invention will become apparent from the following description.

According to one aspect of the present invention, extruded films or sheets are created by extruding a polypropylene having a substantially syndiotactic structure.

The extruded polypropylene, which has a substantially syndiotactic structure, can be a film or sheet with a thickness of 0.005 - 5 mm or a blown film with a thickness of 0.001 - 1 mm.

Description of the preferred embodiments

The term "syndiotactic polypropylene" includes propylene homopolymer and copolymers of propylene and other olefins having 2-25 carbon atoms. Examples of olefins other than propylene include ethylene and olefins having 4-20 carbon atoms and represented by the formula CH₂=CH-R, wherein R is a linear or branched alkyl group having 2-18, preferably 2-12 carbon atoms, including specifically linear olefins, such as butene-1, pentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, pentadecene-1, hexadecene-1, heptadecene-1 and octadecene-1, and branched olefins such as 3-methylbutene-1, 4-methylpentene-1, 4,4-dimethylpentene-1. Repeating units of these olefins may amount to up to 20% by weight, preferably 0-15% by weight, of the corresponding copolymer. These copolymers can provide extruded films and sheets having even better transparency.

The propylene homopolymers having a substantially syndiotactic structure have a syndiotactic pentad fraction of at least 0.7, especially at least 0.8, as measured by 13C-NMR in the form of a solution in 1,2,4-trichlorobenzene. Further, the propylene copolymers having a substantially syndiotactic structure have a peak intensity observed at about 20.2 ppm on a 13C-NMR absorption spectrum measured in the form of a 1,2,4-trichlorobenzene solution using tetramethylsilane as a standard, of at least 0.5, especially at least 0.6 of the sum of all peak intensities corresponding to the respective methyl groups of propylene. Propylene homopolymer whose syndiotactic pentad fraction is smaller than 0.7 does not have sufficient characteristics as crystalline polypropylene, and its physical properties are low. Such a polypropylene homopolymer is therefore not preferred. Propylene copolymers whose Peak intensity ratios, as defined above, smaller than 0.5 not only have poor physical properties but also the problem that extruded articles have a sticky surface.

The molecular weight of the propylene homopolymer or copolymer having a substantially syndiotactic structure may preferably be 0.1-10, more preferably 0.5-5.0, most preferably 0.5-3.0, in terms of intrinsic viscosity measured at 135°C in the form of a tetralin solution. Furthermore, the ratio Mw/Mn of the weight average molecular weight (Mw) of the above homopolymer or copolymer to its number average molecular weight (Mn), both measured by gel permeation chromatography at 135°C, may preferably be from 1.5 to 15.

As a method for producing the propylene homopolymer or copolymer having a substantially syndiotactic structure, the method of J. A. Ewen et al. described above can be exemplified. Any catalysts other than those proposed by Ewen et al. can be used as long as they can produce syndiotactic polypropylene having a syndiotactic pentad fraction of 0.7 or more as a result of polymerization of propylene alone.

The polymerization processes involving the use of the catalysts described above can can also be used to produce copolymers of propylene and other olefins.

Of the methods for producing the propylene homopolymer or copolymer, it is the method involving the use of a polymerization catalyst consisting of a transition metal compound containing an asymmetric ligand and an aluminoxane that gives propylene homopolymers and copolymers having a syndiotactic structure of relatively good tacticity. Examples of the transition metal compound containing an asymmetric ligand include isopropyl(cyclopentadienyl-1-fluorenyl)hafnium dichloride, isopropyl(cyclopentadienyl-1-fluorenyl)zirconium dichloride, and those obtained by replacing one or two of the chlorine atoms with other halogens or C1-5 alkyl groups.

Examples of aluminoxane include compounds formed by

wherein R represents a C₁₋₃-hydrocarbon radical. In particular, compounds in which R is a methyl group and n is at least 5, in particular 10 - 100, are preferably used.

The aluminoxane can be used in an amount of 10 - 1,000,000, preferably 50 - 5,000 moles times the amount of the associated transition metal compound.

No particular limitation is imposed on the conditions for the polymerization. The polymerization may be carried out by solution polymerization in a known inert solvent, by bulk polymerization in a polymerization system substantially free of any inert solvent, or by gas phase polymerization.

The polymerization temperature may usually range from -100ºC to 100ºC, while the polymerization pressure ranges from normal pressure to 101 bar (100 kg/cm²-G). Polymerization at -100ºC to 100ºC under normal pressure to 51 bar (50 kg/cm²-G) is particularly preferred.

By polymerizing propylene alone or propylene and another olefin in the presence of the polymerization catalyst under the polymerization conditions, the propylene homopolymer or copolymer described above can be obtained.

In order to further improve the syndiotacticity fraction of the homopolymer or copolymer, it is advisable to treat the homopolymer or copolymer with a hydrocarbon solvent having 3 - 20 carbon atoms. Examples of the hydrocarbon solvent include propylene itself, saturated hydrocarbons such as propane, butane, pentane, hexane, heptane, octane and nonane, aromatic hydrocarbon compounds such as benzene, toluene, mylol and ethylbenzene, and those obtained by partially or completely replacing their hydrogen atoms with fluorine, chlorine, bromine and/or iodine atoms. Other usable solvents include those which can dissolve or disperse low molecular weight atactic components such as alcohols having 1-2 carbon atoms, ethers having 2 - 20 carbon atoms and esters. No particular limitation is imposed on the manner of washing. Washing is generally carried out at 0 - 100 °C.

Polymerization at a relatively low temperature, generally 100°C or less, in the presence of a catalyst of high purity, normally 90% or higher, is also effective for producing homopolymer or copolymers having a high syndiotacticity fraction.

The propylene homopolymer or copolymer prepared by the process described above and having a syndiotactic structure may be mixed with one or more of various known additives, for example, antioxidants, lubricants, ultraviolet absorbers, ultraviolet stabilizers, heat stabilizers, antistatic agents, organic or inorganic pigments. The resulting composition is granulated if desired, followed by extrusion into various articles. The extrusion method is not particularly limited, and various known methods can be used. For example, to produce a film and a sheet, an apparatus comprising a normal injection molding machine and a mold having a profile required for producing the desired sheet and fitted on the injection molding machine is used. The thickness of the film and sheet of the present invention produced as described above preferably ranges from 0.005 mm to 5 mm. It is preferred to add a nucleating agent to the propylene homopolymer or copolymer of syndiotactic structure before extrusion and/or to cool the thus extruded film or sheet in a special manner, since such a propylene homopolymer or copolymer has a relatively low crystallization rate. The extruded film can also be used as a material for secondary processing such as biaxial stretching or pressure/vacuum punching.

Preferred exemplary nucleating agents include metal salts of aromatic monocarboxylic acids such as benzoic acid, toluic acid and p-tertbutylbenzoic acid; dibenzylidene sorbitols such as 1,3 2,4-di(benzylidene)sorbitol, 1,3 2,4-di(p-methylbenzylidene)sorbitol and 1,3 2,4-di(p-ethylbenzylidene)sorbitol; metal salts of aromatic phosphoric acid compounds such as sodium bis(4-tert-butylphenyl)phosphate and sodium methylene bis(2,4-di-tert-butylphenol)phosphate; high molecular weight compounds with high melting point such as polyvinylcyclohexane, poly-3-methylbutene, crystalline polystyrene and polytrimethylvinylsilane; and quinacridones such as 2,3-quinacridone, dihydroxyquinacridone and acetylated quinacridone. Furthermore, inorganic compounds such as talc, kaolin and mica can also be used with advantage. These nucleating agents can be used alone or in combination.

As a preferred method for cooling an extruded film or sheet, it is sufficient to bring the film or sheet into close contact with conventional cooling rolls. Here, the cooling temperature can be appropriately controlled. In the case of a thick sheet, cooling can be carried out using a medium with a large heat capacity, such as water.

For producing a blown film according to the present invention, it is possible to use a method which is widely used for producing blown polyolefin films. For this purpose, a composition prepared by adding desired additives to the propylene homopolymer or copolymer described above is mixed in a cylindrical shape. An inert gas such as nitrogen is blown into the cylindrical extrudate, thereby stretching the cylindrical extrudate. The cylindrical extrudate thus stretched is smoothed by means of guide plates and then applied to forming rolls. An apparatus constructed by placing a circular die on a conventional extruder is used to extrude the composition in a cylindrical shape. Various other techniques known to those skilled in the art may also be used as required according to the practice of blown film extrusion. The thickness of the blown films of the present invention obtained as described above may generally range from 0.001 mm to 1 mm.

Other extruded articles according to the present invention, for example, tubes, rods and extruded articles of different profiles can be similarly manufactured by methods known to those skilled in the art. Manufacturing processes for these different molded articles are described in detail, for example, in "Oshidashi Seikei (Extrusion)", editor Kenkichi Murakami, Kabushiki Kaisha Plastic Age.

In the present invention, the propylene homopolymer or copolymer having a substantially syndiotactic structure may be partially substituted, for example to an extent of less than 50% by weight, preferably up to 40% by weight, by a propylene homopolymer or copolymer having an isotactic structure. If the proportion of the latter propylene homopolymer or copolymer becomes 50% by weight or more, the impact resistance is reduced. The latter propylene homopolymer or copolymer can be prepared by any of the suitable known methods. Preferably, one having an isotactic pentad fraction of at least 0.9 as measured by 13C-NMR can be used. Extruded articles having high rigidity can be prepared by employing a propylene homopolymer or copolymer having an isotactic structure in place of a portion of a propylene homopolymer or copolymer having a substantially syndiotactic structure.

The present invention will be described in more detail below with the help of examples and comparative examples.

example 1

In an autoclave with an internal capacity of 200 l, 0.2 g of isopropyl(cyclopentadienyl-1-fluorenyl)zirconium dichloride, which had been prepared by converting isopropylcyclopentadienyl-1-fluorene synthesized by a known method into a lithium salt, reacting the salt with zirconium tetrachloride and then recrystallizing the reaction product, and 30 g of methylaluminoxane (degree of polymerization 16.1) were charged. from TOSO-AKUZO CORPORATION and 80 l of toluene. Propylene was then fed to a gauge pressure of 4 bar (3 kg/cm²-G), followed by polymerization at 20ºC for 2 hours.

After completion of the polymerization, the unreacted propylene was purified. To remove inorganic substance, the polymerization mixture was washed with a mixed solvent consisting of 40 l of methanol and 0.2 l of methyl acetoacetate. The thus washed mixture was then further washed with 10 l of 3 wt% hydrochloric acid. The polymerization mixture washed as described above was filtered to obtain 5.6 kg of syndiotactic polypropylene. The syndiotactic pentad fraction of the polypropylene was 0.935 as measured by 13C-NMR, the intrinsic viscosity as measured at 135°C in the form of a tetralin solution was 1.45, and its Mw/Mn as measured in 1,2,4-trichlorobenzene was 2.2.

The polypropylene was mixed with 0.1% by weight of 2,6-di-tert-butyl-p-cresol as a stabilizer and 0.1% by weight of talc as a curing agent and then granulated. A film with a width of 400 mm and a thickness of 0.5 mm was produced using an apparatus consisting of an extruder with a barrel diameter of 40 mm and a downward-facing die mounted on the extruder at 210ºC and a screw speed of 100 rpm. The following physical properties were measured in connection with the above-mentioned film. Physical property Unit Measurement method Turbidity Yield stress Elongation after fracture Yield strength

The film had a haze of 15.5%, a yield stress of 24.6 N/mm² (246 kg/cm²), an elongation after break of 677%, and a yield strength of 590 N/mm² (5900 kg/cm²).

Comparison example 1

A film was prepared in a similar manner to Example 1 except that a commercially available isotactic polypropylene was used which had an isotactic pentad fraction of 0.980 as measured by 13C NMR, an intrinsic viscosity of 2.20 as measured at 135°C in the form of a tetralin solution, and an Mw/Mn ratio of 5.5 as measured in 1,2,4-trichlorobenzene. The film had a haze of 58.7%, a yield stress of 32.6 N/mm² (326 kg/cm²), an elongation after break of 954%, and a yield strength of 1070 N/mm² (18,700 kg/cm²). The strength was good, but the transparency was poor.

Comparison example 2

In a similar manner to Example 1, except that a commercially available propylene-ethylene copolymer having an ethylene content of 4.2 wt.%, measured by

¹³C-NMR, an intrinsic viscosity of 2.26, measured at 135ºC in the form of a tetralin solution and a Mw/Mn ratio of 5.5, measured in 1,2,4-trichlorobenzene, a film was prepared. In a

13C-NMR spectrum of the copolymer, the intensity of an absorption corresponding to the methyl groups of chain units each consisting of five consecutive propylene groups arranged as...mmmm... was 0.931 of the intensity of an absorption corresponding to the whole methyl groups. The film had a haze of 36.5%, a yield stress of 22.7 N/mm² (227 kg/cm²), an elongation at break of 912% and a yield strength of 440 N/mm² (4400 kg/cm²). The film was better in transparency than the film of Comparative Example 1 but inferior in both strength and transparency to the film of Example 1.

Example 2

Polymerization was carried out in a similar manner to Example 1, except that polymerization pressure and temperature were set to 2 bar (1 kg/cm²-G) and 5ºC, respectively, to obtain a syndiotactic polypropylene having a syndiotactic pentad fraction of 0.915 as measured by ¹³C-NMR, a green molar viscosity of 1.71 as measured at 135ºC in the form of a tetralin solution, and an Mw/Mn ratio of 1.9 as measured in 1,2,4-trichlorobenzene. The film had a haze of 12.5%, a yield stress of 26.6 N/mm² (266 kg/cm²), an elongation at break of 720%, and a proof stress of 610 N/mm² (6100 kg/cm²).

Example 3

Into an autoclave with an internal capacity of 200 l were charged 0.1 g of isopropyl(cyclopentadienyl-1-fluorenyl)hafnium dichloride, which was obtained by converting isopropylcyclopentadienyl-1-fluorene synthesized by a known method into a lithium salt, reacting the salt with hafnium tetrachloride (contains 5% by weight of zirconium tetrachloride) and then recrystallizing the reaction product, 0.1 g of isopropyl(cyclopentadienyl-1-fluorenyl)zirconium dichloride (synthesized in a similar manner to Example 1 and purified by recrystallization), 30 g of methylaluminoxane (degree of polymerization 16.1; product of TOSO-AKUZO CORPORATION), 4 l of hexene-1 and 80 l of toluene. Then, propylene was charged to a measuring pressure of 4 bar (3 kg/cm²-G), followed by polymerization for 2 hours at 20ºC.

After completion of the polymerization, the polymerization mixture was treated in a similar manner to Example 1 to obtain a copolymer having a hexene-1 unit content of 6 wt%. According to 13C-NMR, the peak intensity of the copolymer at about 20.2 ppm was 0.68 of the total peak intensity of the methyl groups of the propylene units. This indicated that the copolymer had a substantially syndiotactic structure. Its Mw/Mn ratio was 4.5.

The copolymer was added with the same additives as used in Example 1. A film with a thickness of 0.5 mm was prepared from the copolymer using an extrusion process similar to Example 1. Its physical properties were measured. The following results were obtained.

Turbidity: 8%

Yield stress: (140 kg/cm²) 14 N/cm²

Extension after fracture: 580%

Yield strength: (2 300 kg/cm²)230 N/cm²

Example 4

Using a tubular film extruder with a drum diameter of 40 mm

("BFTK-405", trade name; manufactured by Kawata Seisakusho KK), a blown film having a thickness of 0.005 mm was prepared from the same syndiotactic propylene composition as used to prepare the film in Example 1 at a resin temperature of 240 °C, a cooling water temperature of 20 °C, a take-up speed of 4 m/min, an extruder temperature of 220 °C and a die temperature of 210 °C. The following physical properties were measured. Physical unit Unit Measuring method Turbidity Impact strength Mitsui-Toatsu method* *Under a load, a ball with a diameter of 1/2 inch is made to strike a 10 cm by 10 cm square film of the desired thickness according to the pendulum principle so that the fracture energy when the film breaks can be determined. The impact strength of the film is calculated using the following formula: Fracture energy (kg cm) Impact strength (kg cm/mm) Fracture energy (kg.cm)/film thickness (mm) Elastic modulus Yield stress

The blown film had a haze of 3.7%, an impact strength of 80 kg.cm/mm (23ºC) and 16 kg.cm/mm (-5ºC), a modulus of elasticity of (73 kg/cm²) 7.3 N/mm² and a yield stress of 0.223 N/mm² (2.23 kg/cm²)

Comparison example 3

A blown film was prepared in a similar manner to Example 4 except that a normal isotactic propylene was used which had an isotactic pentad fraction of 0.980 as measured by 13C NMR, an intrinsic viscosity of 1.52 as measured at 135°C in the form of a tetralin solution, and an Mw/Mn ratio of 4.8 as measured in 1,2,4-trichlorobenzene. The blown film showed a haze of 5.0%, an impact strength of 78 kg.cm/mm (23ºC) and 1.5 kg.cm/mm (-5ºC), an elastic modulus of 8.0 N/mm² (80 kg/cm²) and a yield stress of 0.231 N/mm² (2.31 kg/cm²) The tensile strength was essentially unchanged, however, haze and impact strength at low temperature were worse.

Comparison example 4

A blown film was prepared in a similar manner to Example 4, except that a commercially available propylene-ethylene copolymer having an ethylene content of 2.3 wt.% as measured by 13C NMR, an intrinsic viscosity of 1.57 as measured at 135°C in the form of a tetralin solution, and an Mw/Mn ratio of 5.3 as measured

in 1,2,4-trichlorobenzene. In a 13C-NMR spectrum of the copolymer, the intensity of an absorption corresponding to the methyl groups of the chain units, each of which consisted of five consecutive propylene groups arranged as ...mmm..., was 0.965 of the intensity of an absorption corresponding to the entire methyl groups. The blown film had a haze of 5.0%, an impact strength of 82 kg.cm/mm (23ºC) and 18 kg.cm/mm (-5ºC), an elastic modulus of 6.2 N/mm² (62 kg/cm²) and a yield stress of 0.201 N/mm² (2.01 kg/cm²). The low temperature impact strength was improved, but the tensile strength was poor and the haze was poor.

Example 5

A blown film was prepared similarly to Example 4 using the same syndiotactic polypropylene as that used in Example 2.

The blown film had a haze of 3.8%, an impact strength of 85 kg.cm/mm (23ºC) and 24 kg.cm/mm (-5º), a modulus of elasticity of (77 kg/cm²) 7.7 N/mm² and a yield stress of 0.231 N/mm² (2.31 kg/cm²)

Example 6

A blown film was prepared similarly to Example 4 using the same syndiotactic propylene-hexene-1 copolymer used in Example 3.

The blown film had a haze of 1.8%, an impact strength of 95 kg.cm/mm (23ºC) and 35 kg.cm/mm (-5ºC), an elastic modulus of (32 kg/cm²) 3.2 N/mm² and a yield stress of 0.195 N/mm² (1.95 kg/cm²).

Example 7

The procedure of Example 1 was repeated except that 30 parts by weight of a commercially available isotactic polypropylene having an isotactic pentad fraction of 0.962 as measured by 13C NMR and an intrinsic viscosity η of 1.62 as measured at 135°C in tetralin was blended with 70 parts by weight of the syndidotactic polypropylene prepared in Example 1. The resulting film had a haze of 5.2%, a yield stress of 26.5 N/mm² (265 kg/cm²), an elongation at break of 650% and a tensile strength of 710 N/mm² (7100 kg/cm²).

Example 8

Using a polypropylene composition similar to that used in Example 7, a blown film was prepared in a similar manner to Example 4. The blown film had a haze of 3.8%, an impact strength of 75 kg.cm/mm (23ºC) and 16 kg.cm/mm (-5ºC), an elastic modulus of 7.6 N/mm² (76 kg/cm²) and a yield stress of (2.25 kg/cm²) 0.225 N/mm².

Claims (5)

1. An extruded film or sheet formed by extruding a syndiotactic propylene homopolymer having a syndiotactic pentad fraction of 0.7 or more or a syndiotactic propylene copolymer having a syndiotactic pentad fraction of at least 0.5 and containing not more than 20% by weight of olefin units other than propylene units, wherein the olefin units contain 2-25 carbon atoms and the syndiotactic pentad fraction is the ratio of a peak intensity of methyl groups of propylene attributable to the syndiotactic pentad observed at 20.2 ppm on a 13C NMR absorption spectrum based on tetramethylsilane measured in a 1,2,4-trichlorobenzene solution to the sum of all peak intensities corresponding to the respective Methyl groups of propylene are assigned. 2. An extruded film or sheet according to claim 1, each being a sheet having a thickness of 0.005 - 5 mm. 3. An extruded film or sheet according to claim 1, each being a blown film having a thickness of 0.001 - 1 mm. 4. An extruded film or sheet according to claim 3, each being a blown film formed by extruding propylene homopolymer in a cylindrical mold and blowing an inert gas into the cylindrical extrudate. 5. An extruded film or sheet according to claim 2, each being a highly transparent sheet formed by extruding a propylene homopolymer.